Options
UMR Geosciences Azur Villefranche sur Mer, France
4 results
Now showing 1 - 4 of 4
- PublicationOpen AccessVerso una migliore conoscenza delle strutture del margine Ligure: il progetto GROSMARIN(2008)
; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ;Dessa, J. X.; UMR Geosciences Azur Villefranche sur Mer, France ;Bethoux, N.; UMR Geosciences Azur Villefranche sur Mer, France ;Beslier, M. O.; UMR Geosciences Azur Villefranche sur Mer, France ;Hello, Y.; UMR Geosciences Azur Villefranche sur Mer, France ;Anglade, A.; UMR Geosciences Azur Villefranche sur Mer, France ;Desprez, O.; UMR Geosciences Azur Villefranche sur Mer, France ;Fernandez, M. R.; UMR Geosciences Azur Villefranche sur Mer, France ;Manchuel, K.; UMR Geosciences Azur Villefranche sur Mer, France ;Verdier, E.; UMR Geosciences Azur Villefranche sur Mer, France ;Deschamps, A.; UMR Geosciences Azur, CNRS, Sophia Antipolis, France ;Courboulex, F.; UMR Geosciences Azur, CNRS, Sophia Antipolis, France ;Brunel, D.; UMR Geosciences Azur, CNRS, Sophia Antipolis, France ;Klingelhoefer, F.; Ifremer DRO/GM, Plouzane, France ;Bellier, O.; CEREGE, Aix-en-Provence, France ;Lefeldt, M.; IFM-GEOMAR, Kiel, Germany ;Flueh, E.; IFM-GEOMAR, Kiel, Germany ;Solarino, S.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione CNT, Roma, Italia ;Eva, E.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione CNT, Roma, Italia ;Eva, C.; Dipteris, Università di Genova, Italy ;Pavan, M.; Dipteris, Università di Genova, Italy ;Zunino, E.; Dipteris, Università di Genova, Italy ;Scafidi, D.; Dipteris, Università di Genova, Italy ;Spallarossa, D.; Dipteris, Università di Genova, Italy ;Ferretti, G.; Dipteris, Università di Genova, Italy; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; (English Abstract) The Ligurian margin, that is the junction area located between the Ligurian basin and the Southwestern Alps, is a passive margin, seismically active and subjected to gravitative movements. The active deformation in this sector is among the strongest ever experienced in Western Italy and Southern France. The current geodynamics of the basin is not completely understood yet, and somewhat under interest and debate of the scientific community. The latest results on the recent evolution of the Alps-Mediterranean system suggest that the area under study lay close to a domain under extension. The interest for the area is reinforced by its seismic activity that, although of low to moderate energy, acts in an area of high vulnerability. Some historical events involved in fact dramatic social and material damages. The growth of population (that now accounts for more than 2.500.000 inhabitants between Cannes and Genoa), the setting of numerous industries and the tourist business of the area are additional motivation for monitoring the area from the seismic point of view and especially to make specific studies on the seismogenic structures of this sector. Events with magnitude greater than 4.5 to 5.0 are in fact recorded every 5 years, but the area undergoes a rather weak microseismicity that often remains undetected and always poorly located by land seismic networks. The natural risks associated to this sector cannot neglect the presence of steep canyons that incise the offshore margin and favour gravitative slopes. The sediment masses accumulate on top of these canyons and may slip even after an earthquake of moderate magnitude. The GROSMARIN (which stands for GrandROSMARIN) cruise is proposed by UMR Géosciences Azur (with fellow french and italian research groups). It aims at (1) studying the microseismicity along a part of the northern margin of the Ligurian Basin, offshore France and Italy and (2) to realise a 3D tomography by wide-angle seismics. The goal is to better characterize active structures along this zone and to assess the resulting seismic hazard.248 231 - PublicationOpen AccessThe Grosmarin experiment(2008-10)
; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ;Solarino, S.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione CNT, Roma, Italia ;Dessa, J. X.; UMR Geosciences Azur, Villefranche sur Mer, France ;Bethoux, N.; UMR Geosciences Azur, Villefranche sur Mer, France ;Beslier, M. O.; UMR Geosciences Azur, Villefranche sur Mer, France ;Hello, Y.; UMR Geosciences Azur, Villefranche sur Mer, France ;Anglade, A.; UMR Geosciences Azur, Villefranche sur Mer, France ;Desprez, O.; UMR Geosciences Azur, Villefranche sur Mer, France ;Ruiz Fernandez, M.; UMR Geosciences Azur, Villefranche sur Mer, France ;Manchuel, K.; UMR Geosciences Azur, Villefranche sur Mer, France ;Verdier, E.; UMR Geosciences Azur, Villefranche sur Mer, France ;Deschamps, A.; UMR Geosciences Azur, CNRS, Sophia Antipolis, France ;Courboulex, F.; UMR Geosciences Azur, CNRS, Sophia Antipolis, France ;Brunel, D.; UMR Geosciences Azur, CNRS, Sophia Antipolis, France ;Klingelhoefer, F.; Ifremer DRO/GM, Plouzané, France ;Bellier, O.; CEREGE, Aix-en-Provence, France ;Lefeldt, M.; IFM-GEOMAR, Kiel, Germany ;Flueh, E.; IFM-GEOMAR, Kiel, Germany ;Eva, E.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione CNT, Roma, Italia ;Eva, C.; Dipteris, Università di Genova, Italy ;Pavan, M.; Dipteris, Università di Genova, Italy ;Zunino, E.; Dipteris, Università di Genova, Italy ;Scafidi, D.; Dipteris, Università di Genova, Italy ;Spallarossa, D.; Dipteris, Università di Genova, Italy ;Ferretti, G.; Dipteris, Università di Genova, Italy; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ;Slejko, D.; OGS, TriesteThe GROSMARIN (which stands for GrandROSMARIN) cruise is proposed by UMR Géosciences Azur (with fellow french and italian research groups). Its goals are to better characterize active structures along this zone and to assess the resulting seismic hazard in a sort of continuation with respect to the MALISAR experiment, which has already surveyed some active structures through shallow observations. The GROSMARIN cruise is in fact the necessary counterpart to characterize them at depth.188 135 - PublicationRestrictedThree dimensional refraction tomography and accurate seismic locations in the Ligurian Sea from the GROSMarin experiment(2012)
; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ;; The geological evolution of the western Mediterranean exhibits complicated interactions between orogenic processes and widespread extensional tectonics. The region is located in a convergent plate margin separating Africa and Europe, and consists of marine basins – the Alboran Sea, the Algerian- Provençal Basin, the Valencia trough, the Ligurian Sea and the Tyrrhenian Sea- which formed as back-arc basins since the Oligocene. In most reconstructions, it has been stressed that back-arc extension led to drifting of continental blocks and to large-scale block rotations. The opening of the Ligurian Sea. is in fact the result of counterclockwise rotation of Corsica and Sardinia. From the point of view of seismicity, the south western Alps and northern part of the Ligurian basin are subject to frequent earthquakes of low to moderate magnitudes. However significantly destructive events are known to have occurred in the past (e.g. 1564 and 1887). Apart from these rare large events, regional studies agree in concluding that the important local microseismicity appears to be poorly focused (e.g., COURBOULEX et alii, 2007) and that, if some tectonic lines are documented onland (COURBOULEX et alii, 2001), the active structures at sea remain unknown. It is therefore an essential prerequisite to gain better insight into the deep seismogenic structures along the North Ligurian margin and even farther offshore, in the identified oceanic domain. The fact that some of these structures can undergo ruptures of Mw~6.5, such as the 1887 event (BAKUN & SCOTTI, 2006), suggests that, at least to some extent, instrumental insufficiencies in the detection and location of microseismicity is a limit to identify active faults that have not experienced large instrumented ruptures to date. The irregular coverage provided by regional seismic networks produces a bias in the recording of local seismicity. Permanent stations are naturally limited to land areas and fail to properly constrain seismicity offshore. Taking into consideration the peculiarities of regional dynamics (low strain rates, rare large events and a regular seismic activity limited to small events with M < 3-4), even onshore seismicity is insufficiently covered by permanent networks and requires dense temporary instrumenting by mobile stations. Considering the potential threat of strong offshore earthquakes, it is of first importance to characterize faults that are prone to rupture in order to quantify associated seismic and tsunami hazards. Assuming some weak seismicity exists along these faults and remains undetected by onland networks, some marine stations are necessary to address instrumental remoteness and help delineate active structures. Moreover, since the velocity models used for locations are obtained by inverting seismic data and the reliability of their locations depend, in turn, from the quality of the velocity model used for their hypocentral parameters, the constraints on the seismic path provided by a more dense seismic network may contribute to a more accurate reference model. In this study, we profited from the recent developments in sea bottom seismic instrumentation to deploy OBSs above the zones of the North Ligurian to perform seismic shots and obtain the distribution of seismic velocities with 3D active tomography. We also took the opportunity of the long term (6 months) OBSs reduced array to decrease both the detection threshold and recording distances so as to obtain more complete catalogs and better localisations.95 1 - PublicationRestrictedThe GROSMarin experiment: three dimensional crustal structure of the North Ligurian margin from refraction tomography and preliminary analysis of microseismic measurements(2011)
; ; ; ; ; ; ; ; ; ; ; ; ;Dessa, J.-X.; Geoazur, Univ. P. et M. Curie, Univ. Nice Sophia Antipolis, CNRS, IRD, Obs. Côte d’Azur, Quai de la Darse, BP 48, 06235 Villefranche/Mer, France ;Simon, S.; Geoazur, Univ. Nice Sophia Antipolis, CNRS, IRD, Obs. Côte d’Azur, Quai de la Darse, BP 48, 06235 Villefranche/Mer, France ;Lelievre, M.; Geoazur, Univ. Nice Sophia Antipolis, CNRS, IRD, Obs. Côte d’Azur, Quai de la Darse, BP 48, 06235 Villefranche/Mer, France ;Beslier, M.-O.; Geoazur, Univ. Nice Sophia Antipolis, CNRS, IRD, Obs. Côte d’Azur, Quai de la Darse, BP 48, 06235 Villefranche/Mer, France ;Deschamps, A.; Geoazur, Univ. Nice Sophia Antipolis, CNRS, IRD, Obs. Côte d’Azur, Quai de la Darse, BP 48, 06235 Villefranche/Mer, France ;Bethoux, N.; Geoazur, Univ. Nice Sophia Antipolis, CNRS, IRD, Obs. Côte d’Azur, Quai de la Darse, BP 48, 06235 Villefranche/Mer, France ;Solarino, S.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione CNT, Roma, Italia ;Sage, F.; Geoazur, Univ. Nice Sophia Antipolis, CNRS, IRD, Obs. Côte d’Azur, Quai de la Darse, BP 48, 06235 Villefranche/Mer, France ;Eva, E.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione CNT, Roma, Italia ;Ferretti, G.; DipTeRis, Università degli Studi di Genova, Italy ;Bellier, O.; CEREGE, (CNRS UMR 6635, Univ. P. Cézanne Aix-Marseille, IRD, Collège de France), Europole Méditerranéen de l’Arbois, BP 80, 13545 Aix-en-Provence, France ;Eva, C.; DipTeRis, Università degli Studi di Genova, Italy; ; ; ; ; ; ; ; ; ; ; The deep structure of the North Ligurian margin and its contiguous Ligurian basin as well as the seismicity recorded in these zones are neither well understood nor precisely constrained. In order to better address these questions, there is a need for offshore instrumenting, which was realised for a duration of nearly 6 months during the GROSMarin (Grand Réseau d’Observation Sous-Marin) experiment. An array of 21 ocean bottom seismometers was deployed over the most active area of the margin and was complemented on land by mobile seismological stations that densified existing permanent networks. We also realised the acquisition of deep refraction seismic shots at sea in order to get a 3D distribution of velocities along the margin through travel time tomography. We present here a preliminary analysis of the seismicity recorded during this experiment and a tomographic model of the margin structures obtained using data from the offshore network only. Our results support the existence of a high velocity zone at the base of a domain interpreted as transitional between continental and oceanic ones, on the northern part of the deep basin. A very similar pattern is observed across the neighbouring margin of the Gulf of Lions and is most likely related to serpentinisation of the underlying mantle during late rifting and continental break-up. North of this transition zone, we observe the basinward crustal thinning of the continental crust beneath the margin that seemingly narrows eastward. To the south, our results hint at transition to the oceanic domain. In contrast, our velocity distribution does not reveal a transition along strike between transitional and oceanic domains, as previous works suggest. Some microseismic activity was recorded throughout the duration of the experiment, on land and at sea. The number of detected events and precision of location were both improved by our considering French and Italian permanent networks. The detection capabilities of our dense network still need to be fully exploited269 32